Method of blow molding hollow thermoplastic bodies

ABSTRACT

For the blow molding of hollow articles there is provided a receiving station where parisons are prepared, a removing station where the blow molded articles are released from the mold and a depositing station where the articles are placed for transportation or treatment. A mold is movable between the receiving and the removing station and a gripper is movable between the removing and the depositing station. When the mold takes a parison in the receiving station, the gripper grasps a blow molded article in the removing station previously left there by the mold. When the mold opens and releases an article in the removing station, the gripper releases the previously grasped article in the deposition station.

Feb. 27, 1973 R. HOLZMAlNlN ET AL 3,718,724

METHOD OF BLOW MOLDING HOLLOW THERMOPLASTIC BODIES Original Filed April 28, 1969 8 Sheets-Sheet l IN VEN TORS Qaw BY 4640p? Feb. 27, ,1973 R. HOLZMANN ET AL 3,713,724

METHOD OI" BLOW MOLDING HOLLOW THERMOPLASTIC BODIES Original Filed April 28, 1969 8 Sheets-Sheet 2 Feb. 27, 1973 R. HOLZMANN ETAL 3,718,724

MIIJ'I'HOI) 01" LOW MOLDING HOLLOW THERMOPLASTIC BODIES Original Filed April 28, 1968 8 Sheets-Sheet 3 FIG. 7

FIG. 8

Feb. 27, 1973 R. HOLZMANN A METHOD OF BLOW MOLDING HOLLOW THERMOPLASTIC BODIES 8 Sheets-Sheet &

Original Filed April 28, 1.969

FIG. 10

Feb. 27, 1973 R. HOLZMANN ETA!- 3,713,724

METHOD OF BLOW MOLDING HOLLOW THERMOPLASTIC BODIES Original Filed April 28, 1969 8 Sheets-Sheet 5 Feb. 27, 1973 R. HOLZMANN ETAL 3,718,724

METHOD OF BLOW MOLDING HOLLOW THERMOPLASTIC BODIES Original Filed April 28, 1969 8 Sheets-Sheet 5 FIG. 73

Feb. 27, 1973 v R. HOLZMANN T I 3,718,724

METHOD U1" BLOW MOLDING HOLLOW THERMOPLASTIC BODIES Original Filed April 28. 1969 s Sheets-Sheet 7 Feb. 27, 1973 R. HOLZMANN ETAL 3,718,724

METHOD OF BLOW MOLDING HOLLOW THERMOPLASTIC BODIES ori inal Filed April 28, 1969 8 Sheets-Sheet 8 FIG. I7

1 FIG. 78 572 528 544 5280 545\ 5280 573 52 r b4 i 570 k 577 I W W- V V H United States Patent U.S. Ci. 264-98 Claims ABSTRACT OF THE DISCLOSURE For the blow molding of hollow articles there is provided a receiving station where parisons are prepared, a removing station where the blow molded articles are released from the mold and a depositing station where the articles are placed for transportation or treatment. A mold is movable between the receiving and the removing station and a gripper is movable between the removing and the depositing station. When the mold takes a parison in the receiving station, the gripper grasps a blow molded article in the removing station previously left there by the mold. When the mold opens and releases an article in the removing station, the gripper releases the previously grasped article in the depositing station.

This is a divisional application of application Ser. No. 819,724, filed Apr. 28, 1969, now US. Pat. No. 3,583,- 031, issued June 8, 1971.

BACKGROUND, OBJECTS AND SUMMARY OF THE INVENTION This invention relates to a method of blow molding hollow articles, such as bottles, capsules or tubes from thermoplastic materials. Conventionally, an apparatus for practicing such a method includes a two or multi-part hollow blow mold which is adapted to be moved backwards and forwards between a receiving station where it accepts a tubular parison from the nozzle of an extruder and a removing station where the hollow blow molded body is released from the mold. The apparatus further includes means-such as a blowing mandrelto admit pressure into the mold for expanding the parison and thus forming said blow molded body.

It is an object of the invention to provide an improved method of the above type wherein the blow molded hollow articles are transmitted from said apparatus to a subsequent conveying or treating device in an orderly sequence.

Briefly stated, the method according to the invention comprises the following steps: moving the mold back and forth between a receiving station (where the mold is charged with a parison) and a removing station (where the finished article leaves the mold) and moving an article gripper back and forth between said removing station and a depositing station (Where the article leaves the gripper); the mold and gripper displacements are effected in unison and in synchronism by one and the same displacing means; opening and closing said mold and said gripper in each station in unison by one and the same actuating means, so that in a coordinated, overlapping sequence the mold carries the parison from the receiving station and leaves the finished, expanded article in the removing station, while the gripper carries the finished 'ice article from the removing station and leaves it in the depositing station.

The invention will be better understood and further objects as well as advantages will become more apparent from the ensuing detailed specification of several exemplary embodiments taken in conjunction with the schematic drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view of one embodiment of the invention;

FIG. 2 is a view corresponding to FIG. 1, showing the embodiment in a different operating position;

FIG. 3 s a front elevational view of the support element for the mold parts taken along line II of FIG. 1;

FIGS. 4 to 6 are side elevational views of three working positions of another embodiment of the invention;

FIGS. 7 and 8 are side elevational views of two working positions of a further embodment;

FIGS. 9 and 10 are side elevational views of two Working positions of still another embodiment;

FIGS. 11 and 12 are side elevational views of two working positions of a further embodiment;

FIGS. 13 to 15 are plan views of still a further embodiment in three working positions;

FIG. 16 is an enlarged side elevational view of a detail of FIG. 14;

FIG. 17 is an enlarged longitudinal sectional view of a mold of the last-named embodiment; and

FIG. 18 is a side elevational view of a conveyor for the finished articles.

DESCRIPTION OF THE EMBODIMENTS In the different embodiments now to be described, parts having substantially the same function are assigned reference numerals having identical last two digits.

The embodiment shown in FIGS. 1 to 3 includes an extruder 10 which is provided with an extrusion head 11 having a downwardly directed annular extrusion nozzle, from which the tubular parisons 12 are extruded. These parisons are received in sections by a hollow mold 113, comprising two halves 13a, 13b which are carried by plate-like supports 29a, 29b and which are movable relatively to one another. The mold halves are driven by means of hydraulic cylinders 14a, 14b, which are arranged on an upwardly open, U-shaped support element 18, which absorbs the forces resulting from the blowing pressure during the expanding of the parisons 12.

Situated laterally alongside the extrusion head 11 is a station 15, where the parisons are expanded in the hollow mold 13 and the obtained hollow bodies 28 are removed therefrom. The station 15 comprises essentially a blowing and gauging mandrel 16, which can be moved up and down by a cylinder 17. Thus, it is seen that the mold 13 and mandrel 16 are arranged independently of one another. The mold 13 is arranged to be displaceable backwards and forwards between a first position below the extrusion head 11 (receiving station) and a second position at the station 15 (removing station). For this purpose, the support element .18 is connected by pivoting links 23 to a machine frame 24, and executes, with the mold 13, a swinging movement between the extrusion head 11 and station 15, as indicated by the arrows 19 and 20 in FIG. 1. This swinging movement is caused by a cylinder 21, the piston rod 22 of which is connected with a projection of the support element 18.

Secured to the mold halves 13a, 13b, or to the support members 29a, 2912, are arms 25 which carry at their ends remote from the mold 113, grippers 26a, 26b forming together a gripper device 26. The grippers 26a, 2612, which are operated in the opening and closing direction in synchronism with the two mold halves 13a, 1312, may be constructed as a supporting and cooling mold. In addition, a conveying arrangement in the form of an endless conveyor belt 27 is provided.

In the first position as shown in FIG. 1, the mold 13 is situated beneath the extrusion head 11. First, it is opened so that the tubular parison 12 will extend between the two mold halves 13a, 13b. The mold is then closed by operating the cylinders 14a, 14b and is swung in the direction of the arrow 20 into the second position (FIG. 2) where the station 15 is located. The blowing mandrel 16 is now forced downwardly into the mold and into the upper end of the parison disposed therein. Then, compressed air is introduced into the parison which is expanded until it bears against the wall of the mold. The hollow article 28 thus produced cools inside the mold, resulting in the solidification of the thermoplastic material. Thereafter, the mold :13 is opened by moving the two mold halves apart, while the hollow article remains suspended from the mandrel 16.

Meanwhile, the successive parison 12 is extruded from the extrusion head 11. If now the mold 13 is swung back in the direction of the arrow 19 to the extrusion head 11 for the purpose of receiving the said successive parison, the grippers 26a, 26b, by virtue of their attachment to respective mold halves 13a, 1315 by means of arms 25, participate not only in the opening and closing movements of the mold 13, but also in the pivotal displacements thereof in the direction of the arrows 19 and 20, reach the station 15. By this time the two halves 26a, 26b of the gripper device 26 have been moved apart, thus, the gripper 2 6 is opened. If now, actuated by the cylinders 14a, 14b, the two mold halves 13a, 13b are moved towards one another until the mold 13 is closed, the gripper device 26 is also closed so that its two halves 26a, 2612 are positioned around and grasp the previously produced hollow article 28 depending from the mandrel 16. The mandrel 16 may then be upwardly withdrawn by the cylinder 17 from the hollow article since the latter is now held by the gripper device 26. With the subsequent swinging displacement of the mold 13 in the direction of the arrow 20, the gripper 26 with the hollow body 28 contained therein is brought into the second position (depositing station) immediately above the conveyor belt 27 (FIG. 2). As soon as the mold 13, now disposed at the station 15, is opened, the two halves of the gripper 26 are also moved apart, so that the hollow article 28 disposed therein drops on the conveyor belt 27 and is carried away thereby. In this way, it is thus possible to transfer without any ditficulty the hollow articles to the conveyor belt 27 in an orderly sequence and to advance them to a subsequent treating apparatus or the like.

As has already been stated, the U-shaped support element 18 takes up the forces which appear in the mold during the blowing of the parisons. These forces, the strength of which depends substantially on the level of the blowing pressure and the surface acted upon by said pressure, are in particular very strong, as is generally usual today, if the mold is provided with several mold cavities and thus several parisons are expanded simultaneously. In order to be able to absorb these substantial forces, the support element must be of a correspondingly robust construction, which, in turn, results in a very heavy and cumbersome structure. Furthermore, considerable energy has to be spent for the forward and backward movement of such support element with the mold between the two stations. For these reasons, it is often preferable to use transversal bars on which the mold parts may slide.

Turning now to the embodiment shown in FIGS. 4 to 6, again, there is provided an extruder 110 with an extrusion head 111 and a removing station 115, in which the hollow articles are likewise expanded. Also, a blowing mold 113 is provided, the two halves of which are movable relatively to one another perpendicularly to the plane of the drawing. It is to be noted that in FIGS. 4-6 the observer views directly the rear half 1 13b of the mold.

Again, the mold halves may be driven by hydraulic cylinders (not shown), which act on plate-like supports 129 which carry the mold halves and which are linearly displaceable therewith.

The mold carried by the supports 129 is arranged to be movable linearly in a horizontal plane backwards and forwards between the extrusion head 111 and station 115. The mold may thus be brought from its position shown in FIG. 5 in the direction of the arrow 120 into the position shown in FIG. 4, in which it is positioned at the station beneath the blowing mandrels 116. From the position shown in FIG. 4, the mold 113 is adapted to be returned in the direction of the arrow 119 into the initial position according to FIG. 5. FIG. 6 shows an intermediate position of the mold between the receiving station and the removing station.

As a departure from the embodiment of FIGS. 1 to 3, parallel to the opening and closing movements of the mold halves and of the supports 129, there are disposed bars 131a, 131b serving to guide the said supports and thus the mold halves during their opening and closing movements. In addition, the function of these bars is to strut the entire assembly and to take up the forces which are present during the expansion of the parisons 112 and which tend to separate the mold halves. The presence of these bars requires certain measures in order to ensure that the hollow bodies 128, temporarily remaining in the removing station 115 after the mold is open, do not interfere with the return movement of the mold in the direction of the arrow 119 towards the extrusion head 111. The two bars 131a, 131b are arranged diagonally with respect to supports 129 in such a manner that the bar 131a which is leading during displacement in the direction towards the station 115 (Le, in the direction of the arrow 120), is positioned lower than the bar 131b. The result of this arrangement is that, during the return movement of the mold 113 in the direction of the arrow 119, the lower bar 131a is moved past the hollow articles 128 suspended from the mandrels 116 in station 115, so that the hollow articles do not interfere with the movement of the mold and the support 118, as in the precedingly described embodiment. Consequently, it is again not necessary to remove the hollow articles 128 from the mandrels immediately after the opening of the mold 113 at the removing station 115 in order to permit the mold to perform its return movement in the direction of the arrow 119. The return movement of the mold 113 may, in fact, take place regardless of whether or not hollow articles are still in the station 115.

Since two parisons 112 are simultaneously extruded, the mold 113 is provided with two mold compartments 130 which are arranged side-by-side. As a consequence, two hollow articles 128 are produced simultaneously in a single operation. Therefore, in the station 115 two blowing mandrels 116 are provided which are moved vertically in either direction by cylinders 117.

In addition, the embodiment according to FIGS. 4 to 6 is provided with a feed worm or screw 132 which is adapted to be moved axially backwards and forwards inside the housing 133. This construction allows the worm 132 to rotate continuously, the material being initially delivered into a storage chamber 134 immediately downstream of the free end of the worm 132. As soon as the material necessary for forming the parison has accumulated in the storage chamber 134, the screw 132 is.

displaced in the direction of the arrow 135 (FIG. 5) so that the material which is in the storage chamber 134 is rapidly extruded downwardly through the extrusion head 111 and the extrusion nozzles disposed therein. The extrusion of the parisons 112 thus takes place intermittently. The linear forward displacement of the screw 132 occurs approximately at that moment in which, during the return movement of the mold 113 in the direction of the arrow 119, bar 131b has passed all extrusion nozzles of the extrusion head 111. In this way, a rapid operating cycle is obtained. This procedure is based on the assumption that the extrusion of the parisons 112 only takes a short time.

After the parisons 112 have attained the required length, the mold 113 is closed and is displaced in the direction of the arrow 120 until it reaches the removing 'station 115. At this station, the blowing and gauging mandrels 116 are introduced downwardly into the mold and thus into the parisons, whereafter the latter are expanded until they bear against the wall of the mold. After adequate cooling and solidification of the material, the mold 113 is opened, while the hollow articles 128 remain suspended from the mandrels 116. In the course of the return movement of the mold 113 in the direction of the arrow 119, a gripper 126 enters the removing station 115 (FIG. As in the embodiment of FIGS. 1 to 3, this gripper device consists of two parts, each of which is connected through an arm 125 to the supports 129 carrying the mold halves. After the gripper device has reached the station 115 and has thus assumed the position shown in FIG. 5, it grasps the hollow articles 128 suspended from the mandrels 116 during the closing movement of the mold 113 which is then disposed beneath the extrusion head 111. The two mandrels 116 may then be withdrawn in an upward direction from the hollow articles so that the gripper device 126 may thereupon bring the hollow articles, by virtue of a subsequent movement in the direction of the arrow 120, to the successive depositing station 136, in which the hollow articles may be subjected to a desired treatment or handling. Indicated at 137 are tubes which receive the hollow articles after the gripper device 126 has been opened in the depositing station 136.

Turning now to the embodiment shown in FIGS. 7 and 8, an extrusion head 211 and a removing station 215, where the hollow bodies are expanded and then released by the mold, are again provided. The blow mold 213 is displaceable in either direction between the extrusion head 211 and the station 215 along an arcuate path by means of links 223. At one end, the links 223 are pivotally secured to a machine frame, while at the other end they are pivotally attached to bars 231a, 2311b which interconnect the mold carrier supports 229 and extend parallel to the opening and closing movements of the mold halves 231a and of the supports 229. The arrangement of the two bars 2310, 231b is the same as in the embodiment according to FIGS. 4 to 6.

Furthermore, the supports 229 are provided, in a manner already described, with arms 225 which carry at their ends complemental parts forming a gripped device 226. The arrangement is such that the gripper device 226 is situated in the removing station when the mold assumes a position beneath the extrusion head 211.

The aforenoted arrangement of the bars 231a, 231b, together with the method of moving the mold 213 between the two stations 211 and 215 in an arc of an approximate extent of a quarter of a circle, has the result that, during the return movement in the direction of the arrow 219 from the removing station 215 towards the extrusion head 211, the bar 231a follows a path 240 which passes beneath the space occupied by the hollow articles 228 suspended from the mandrels 216 inside the removing station 215. Here, again, the hollow articles 228 may remain on the mandrels without interfering with the movement of the mold 213 towards the extrusion head 211 in the direction ofthe arrow 219.

Also, it is a significant feature here that the path f movement 241 of the upper bar 231b passes beneath the parisons 212, which have meanwhile been extruded in a continuous extrusion process. It is thus seen that in this embodiment the extrusion of the parisons may take place continuously, unlike in the embodiment according to FIGS. 4 to 6. Otherwise, the course of the manufacturing procedure substantially conforms to that of the last named embodiment.

In the embodiment according to FIGS. 7 and 8, the depositing station 236, which is situated after the removing station 215, includes a device 242 for detaching the pieces of waste or flash 243, 244 from the hollow articles 228. This device comprises essentially two rotary impact cutters 245, 246 which are carried by a common support 247, which, in turn, may be reciprocated in the direction of the arrows 248, 249. The upper rotary cutter 245 is associated with the flash 243 on the neck of the bottle and is displaceable along its axis of rotation 250. The lower cutter 246, which is associated with the flash 244 on the bottom of the hollow body 228, is movable transversely of its axis of rotation 251. It is obvious that the knives may be arranged differently, for example, in such a manner that both cutters are displaceable in the direction of their axis of rotation or transversely thereof. The choice of the arrangement will in each case depend on the type and configuration of the flash, the space available, and other factors. The cutters, which are respectively driven by motors 252 and 253, rotate at high speed. During the displacement in the direction of the arrow 248, the knives hit the flash 243 and 244, connected only by a narrow web to the associated hollow article 228, and thus readily separable therefrom upon contact with the respective cutter. On completing the severing operation, the knives return in the direction of the arrow 249 into their initial position shown in FIG. 8.

A further embodiment is shown in FIGS. 9 and 10. Here, the blowing and gauging mandrels 316, which are arranged in a removing station 315 and are adapted to e moved vertically up and down by means of cylinders 317, project from below into the mold 313 and into the parisons 312 disposed therein. Accordingly, in order to permit the hollow bodies 328 to remain in the removing station 315 While the mold 313 returns to the extrusion head 311, the bars 331a and 331b are oppositely arranged when compared with previously described embodiments. They are diagonally arranged as before, but here the bar 331a which leads during the displacement in the direction towards the removing station 315, is the upper bar while bar 331]; is the lower bar. The result of this arrangement is that, r gardless of the type of movement which the mold 313 executes between the two stations, the leading bar 331b, during the return from the removing station 315 to the extrusion head 311, follows a path which is below the space into which the parisons 312 are extruded for the successive cycle. The trailing bar 331a during the return movement from the station 315 to the injection head 311 follows a path which remains above the space occupied by the hollow articles 328 disposed in the removing station 315. It is of no consequence whether this path of movement is linear, as indicated by the broken line 340, or curved, as indicated by the broken line 340a. Even in case of a horizontal movement of the mold 313, the bar 331a will not interfere with the hollow bodies 328 which are still in the removing station 315 and are impaled on mandrels 316. Similarly to the other embodiments, the supports 329 for the mold halves 313a are provided with projections or arms 25, which, at their free ends, form a gripping device 326. The parts in this embodiment cooperate in a manner similar to the previously described structures. The fact that the structure shown in FIGS. 9 and 10 comprises three mold cavities 330 and thus three mandrels 316 is of no significance, since the number of molds and thus the number of simultaneously extruded parisons does not affect the practicing of the invention.

Turning now to the embodiment shown in FIGS. 11 and 12, the structure depicted therein differs from the previously discussed embodiments in that the mandrel-s 416 arranged in the removing station 415 are displaceable to such an extent that the hollow bodies carried thereby are moved out of the path of travel of the mold 413. In all other significant details this embodiment is identical to the structures already described.

As in the other embodiments, the mandrels 416 are carried by cylinders 417, but are vertically movable to a considerably greater extent. After the mold 413 is opened in the station 415 by moving the two mold halves apart, the mandrels 416, together with bodies 428, are m ved upwardly in the direction of the arrows 454 to such an xtent that the lowest outer faces of the hollow articles will be disposed above the bar 431a, which is the trailing bar during movement of the mold 413 from the removing station 415 back to the extrusion head 411. It is thus seen that the upper bar 431a may pass unobstructed below the raised bodies 428. The bar 431b, which is the leading bar during this displacement of the mold 413, is also the lower bar, so that a continuous extrusion of the parisons 412 from the extrusion head 414 may take place. Here, again, the displacement of the mold between the two Stations may follow a linear or a curved path 440 or 440a, respectively.

It is also possible to arrange the mandrels, similarly to the embodiment of FIGS. 9 and 10, in such a manner that they project from beneath into the mold and into the parisons disposed therein. It is apparent that in such an arrangement the afore-described movement of the mandrels to remove the hollow articles from the path of the mold, would be directed downwardly.

As seen in FIG. 11, the gripper device 426, which is arranged on arms 425 carried by the supports 429, grasps the hollow articles 428 in their raised position which they assumed due to the upward displacement of mandrels 416. After the gripper device 426 is closed in the course of the closing movement of the mold (disposed beneath the extrusion head 411) and thus securely holds the hollow articles 428 still attached to the mandrels 416, the latter may now be withdrawn from the hollow articles 428 with a second and normally shorter upward movement. With a subsequent movement of the mold 413 into the blowing and removing station 415, the gripper device 426, with the hollow articles 428 disposed therein, is brought into the position (depositing station) shown in FIG. 12. There, an additional station 436 may be provided in which any desired finishing operation may be per-formed on the hollow articles 428.

The afore-described design does not involve a more complex structure or a significant increase in costs. Since the mandrels have to be vertically movable in any case to penetrate into the parison and then withdraw from the blow molded article, merely the path of travel for the mandrels is increased. This embodiment is particularly adapted for use in already existing, subsequently converted machines.

It is seen that the precedingly-described embodiment is designed in such a manner that the displacement of the blow molded article immediately after opening of the mold is effected linearly in its length dimension. It is noted that a displacement in the said direction exerts the least stress-if any at all-on the often still malleable hollow article. This is an advantageous feature since it is often a desideratum to open the mold as soon as possible, thus, at an early moment when the hollow article is not yet completely solidified.

FIGS. 13l7 show another embodiment of the invention, which differs from the previously discussed structures first, by the arrangement of the mandrel and secondly, by the design of the gripper device.

As seen in FIG. 17, the blowing mandrel 516 projects from below into the mold 513, which, as before, consists of two halves 513a, 5131;. Contrary to all other embodiments, however, the mandrel 516 participates in the reciprocating motion of the blow mold 513 between the two stations, that is, between the extruder and the removing station. For this reason it is necessary to provide the removing station with an auxiliary support mandrel 555 (FIGS. 13, 14, 16 and 17) which may be moved up and down longitudinally. In the removing station 515, the auxiliary mandrel 555 assumes the function of holding the hollow article 528 after the mold has been opened, until the gripper device 526 reaches the removing station, closes and thus securely grasps the hollow article carried by the auxiliary mandrel.

The two mold halves 513a and 513b, or their supports 529 are provided with arms or projections 525 which, with their free ends, are in engagement with carriages 556 mounted in frame supports 557. The latter also carry grippers 526a, 52617 aflixed to their sides which face one another. The supports 557 are provided with rods 558 which extend parallel to the opening and closing directions of the mold 513 and of the grippers 5261:, 526b and which serve as guide rails for the sliding motion of carriages 556. In each frame support 557, between the carriage 556 and the aforenoted side of support 557 there are disposed helical springs 559 each surrounding a rod 558. The supports 557 are movable in the opening and in the closing direction on guides 560 connected in a suitable manner to the machine frame 524, to which there is also aflixed an abutment 561. A nose 562 integral with each support 557 cooperates with the abutment 561 so that the movement of the supports 557 in the closing direction is limited.

The carriage 556 disposed on the left in FIGS. 13 to 15 is provided on its side facing the associated gripper part 526a with a stripper device 563 rigidly attached to carriage 556 by two pins 564.

In the position of the parts as shown in FIGS. 13 to 17, the mold 513 is disposed in the receiving station, i.e. beneath the extrusion head (not shown), and the gripper device 526 is at the removing station, with which the auxiliary mandrel 555 is associated. Since in this embodimentsimilar to the embodiment according to FIGS. 1 to 3 only a single article is made during each cycle, the mold 513 has only one mold cavity 530 and also, only one auxiliary mandrel 555 is provided. It is to be understood that if mold 513 has a plurality of mold cavities, then a correspondingly increased number of auxiliary mandrels should be used.

Initially, the mold 513 and the gripper device 526 are completely open (FIG. 13). At this time, a parison extends downwardly from the extrusion head (not shown) and is received by the mold. As soon as the mold 513 reaches the removing station 515, the auxiliary mandrel 555, operable by a cylinder 517, is introduced from above into the flash 544 (FIG. 17). At this time, the flash is still plastically deformable, so that if the auxiliary mandrel 555 has surface irregularities, a positive connection ma be established between the auxiliary mandrel 555 and the flash S44, and thus also with the hollow article 528 with which the flash 544 is connected through a thin web 565. Immediately after the forcible insertion of the auxiliary mandrel 555 into the flash 544, the parts assume the position shown in FIG. 17 and the article 528 is formed by blow molding. Thereafter, the mold 513 may be opened which is preferably preceded by the withdrawal of mandrel 516 from the mold and the hollow article 528.

The hollow body 528 disposed in the removing station is now held solely by the auxiliary mandrel 555, since, as already stated, the precedingly withdrawn blowing mandrel 516 participates with the mold 513 in the reciprocating movement between the extrusion head and the removing station.

It is to be noted in this connection that an auxiliary mandrel of the type described above and indicated at 555 may also find application in an apparatus where the blowing mandrel does not travel with the mold. Thus, in assemblies where the blowing mandrel is arranged above the mold, an auxiliary supporting mandrel may be provided which cooperates with the lower portion of the hollow article disposed in the mold.

During the closing movement towards the position shown in FIG. 14, first both the carriages 556 and the supports 557 move synchronously with the two mold halves 513a, 513b. This is achieved by suitably selecting the strength of the springs 559, which are not compressed during this first phase of the closing operation, approximately until the position shown in FIG. 14 is reached. Thus, the displacement of the carriages 556 by the two respective mold halves 513a, 5131) also results in a corresponding displacement of the supports 557, which proceeds until the two gripper parts 526a and 5261) arrive into engagement with the hollow article 528 disposed in the removing station 515. By this time the mold 513 is still not completely closed (FIG. 14). As the two mold halves 513a, 513b continue to move in the closing direction, the carriages 556 are now caused to slide on rods 558, thus compressing the springs 559. Stated in different terms, each carriage 556 is displaced in relation to the associated support 557 until the terminal position shown in FIG. 15 is reached. The mold 513 is now completely closed. During this last phase of the closing operation, the position of the gripper parts 526a, 52Gb has not changed. The force of springs 559 is so chosen that in no case is there a transmission of forces to the hollow body which may cause an unpermitted deformation thereof. Due to advance motion of the gripper parts with respect to the mold halveswhich results in a grasping of the hollow article by the gripper device in the removing station prior to the full closing of the mold halves in the receiving station-it is possible to withdraw the blow mandrel from the hollow body or the auxiliary mandrel from the flash before the mold halves are completely closed. Thus, the mold, immediately after its closing, may be moved from the extrusion head of the receiving station towards the removing station.

The stripper 563 secured to the left hand carriage 556 participates in the entire closing movement. Thus, during the second phase, in which the gripper parts 526a, 52Gb are already in engagement with the hollow article 528, the stripper 563 is displaced in relation to the gripper parts and the hollow article. It is particularly well seen in FIG. 16 that the stripper 563 is moved past the article 528 very close to its base 566 so that the stripper 563, in said second phase, positively abuts the flash 544 and tears it off the base 566 of the hollow article 528. It is noted that the auxiliary mandrel 555 has been introduced into the flash 544 only to such an extent that free passage of the stripper 563 between the base 566 and the lower terminus of auxiliary mandrel 555 is ensured.

Since, as already mentioned, the auxiliary mandrel 55S serves essentially for holding the hollow body 528 after it has been removed from the mold and before it is securely engaged by the gripper device 526, the auxiliary mandrel 555 may already be withdrawn upwardly at the moment in which the parts assume approximately the position according to FIG. 14. As soon as this position is reached, the auxiliary mandrel 555 is no longer required as a holding means for the hollow article 528. Nevertheless, it is generally desirable to retract the auxiilary mandrel 555 upwardly only after completion of the separating operation affecting the fiash 544, since the auxiliary mandrel holds the said waste material in a particularly suitable position for the separating operation. In particular, the auxiliary mandrel 555 prevents the flash from being folded over under the action of the stripper 563; this is a distinct possibility if the plastic material is still soft.

It is nevertheless possible to withdrawn the auxiliary mandrel 555 before the mold 513 is completely closed. Thus, the mold 513 may be moved from the receiving station into the removing station 515 immediately following the closing operation. Simultaneously, the previously produced hollow article 528, freed from the flash 544 by the stripper 563, is moved, carried by the gripper 526, so that the removing station 515 is empty when the mold 513 returns thereto and assumes a position similar to that shown in FIGS. 3, 4, 8, 10 and 12, with the difference, however, that the blowing mandrel 516 is connected to the mold 513 and projects into the latter from below. Furthermore, this arrangement also provides the possibility of commencing the expanding of the hollow body immediately after closing the mold in the receiving sta- 10 tion, so that the station 515 only serves for removing the hollow articles from the mold, whereas in all other embodiments, the removing station also functions as the blowing station.

The gripper device engaging the hollow articles in the removing station is particularly adapted to deliver the hollow articles in an orderly sequence to a subsequent conveyor, while at the same time, the hollow articles may be subjected to any other processing operation.

Turning now to FIG. 18, there is shown a conveyor particularly adapted to be used in the aforenoted environment. The conveyor track comprises a pair of horizontally spaced upper rails 570 and, therebelow, a pair of horizontally spaced lower rails 571. The hollow article 528 engaged by the gripper device 526 is pushed into one end of this track whereby the precedingly inserted hollow articles 528a are intermittently advanced in the direction of the arrow 572.

After the gripper device 526 has pushed the hollow article 528 into the receiving end of the conveyor track, it is opened at the moment when the successive hollow body situated in the removing station is released from the mold. Simultaneously with the subsequent return movement of the mold into the receiving station, the now open gripper device 526 is once again returned in the direction of the arrow 573 into the removing station, where it grasps the successive hollow article in the manner previously described.

The two pieces of flash 543 and 544 on the article are detached during the forward movement of the article in the track by rotating impact cutters 545 and 546 arranged in a stationary manner above and below the conveyor.

In all of the above-described embodiments the working faces of the gripper devices may be provided with a resilient lining (rubber, foam plastic, or the like) to ensure a gentle engagement of the hollow articles.

Summarizing the most significant advantages obtained by the invention, it is seen that individual operational steps may be performed simultaneously without hindrance from one another. In particular, the invention permits, without the least increase in structural costs, a handling of the hollow articles in such a manner that said articles are transmitted to subsequent stations in an orderly sequence and may be submitted to additional treatments without thereby rendering the apparatus or the operation more complex. It is a significant feature that despite a temporary retention of the hollow article in the removing station, the productivity of the apparatus is not decreased.

What is claimed is:

1. A method of blow molding hollow articles of thermoplastic material comprising the following cyclically repetitive steps:

(a) moving an empty mold to a receiving station where parisons are extruded and moving a gripper from a depositing station to a removing station where a first blow molded article released from said mold during a preceding cycle is supported, the movement of said empty mold and the movement of said gripper being effected in unison by a common, sole displacing means,

(b) closing said mold about a parison and closing said gripper about said first blow molded article in unison by a common, sole actuating means,

(c) moving said mold towards said removing station and moving said gripper with said first blow molded article towards a depositing station in unison by said displacing means,

(d) expanding said parison in said mold to form a second blow molded article,

(e) opening said mold in said removing station for leaving said second blow molded article therein and opening said gripper for releasing said first blow molded article in said depositing station in unison by said actuating means and (f) supporting said second blow molded article in said removing station.

2. A method as defined in claim 1, wherein subsequently to step (b) but prior to step (d) a blowing mandrel is introduced into said mold through said parison.

3. A method as defined in claim 2, wherein in step (f) said second blow molded article is supported on said blowing mandrel until engaged by said gripper during step (b) of the successive cycle, whereupon said blowing mandrel is withdrawn from said second blow molded article.

4. A method as defined in claim 3, wherein subsequently to step (f), but prior to step (a) of the successive cycle, said blowing mandrel is longitudinally displaced in said removing station together with said second blow molded article, said gripper, during step (b) of the successive cycle, engages said second blow molded article in said longitudinally displaced position.

5. A method as defined in claim 2, wherein subsequent to step (b), but prior to step (e), an auxiliary support mandrel is introduced into said thermoplastic mate- 12 rial, said blowing mandrel is withdrawn from said second blow molded article subsequent to step (d), but not later than step (a) of the successive cycle; in step (t) said second blow molded article is supported on said auxiliary mandrel until engaged by said gripper during step (b) of the successive cycle.

References Cited UNITED STATES PATENTS 6/1967 Mehnert 264-498 X 5/1968 Hagen 264-94 X US. Cl. X.R. 26499 

